Restraint stress promotes monobenzone-induced depigmentation in mice via the activation of glucocorticoid receptor/macrophage migration inhibitory factor signaling pathway

Psychological stress triggers onset and development of vitiligo in humans. However, the mechanism of psychological stress on vitiligo remains unclear. The study aims to investigate whether psychological stress promotes vitiligo and explore the underlying mechanism. A depigmentation mouse model induced by applying a skin-bleaching reagent monobenzone to dorsal skin and an in vitro HaCaT keratinocyte death model induced by monobenzone were employed to explore the effect of restraint stress, which mimics psychological stress, on depigmentation. The results indicated that restraint stress promoted vitiligo-related depigmentation, vacuolisation, spongiosis, CD8+ T lymphocyte infiltration, and loss of melanocytes in the skin. Restraint stress activated cutaneous NLR family containing pyrin domain protein 3 (NLRP3) inflammasome. In addition, restraint stress aggravated anxiety-like behaviors and increased levels of macrophage migration inhibitory factor (MIF) and corticosterone in the circulation, accompanied with decreasing the expression of cutaneous 8-oxoguanine DNA glycosylase (OGG1) in depigmentation mice. In vitro experiments demonstrated that activation of glucocorticoid receptor (GR) by cortisol upregulated NLRP3 expression dependent on MIF, and directly decreased the transcription of OGG1. Blockade of MIF reversed the NLRP3 signal in restraint stress-induced depigmentation mice. In conclusion, restraint stress promotes vitiligo-related depigmentation in mice via the activation of GR/MIF signaling pathway. The findings provide a theoretical basis for prevention and treatments of vitiligo with therapies of targeting GR, MIF, and OGG1.

Profiling of Barley, Wheat, and Rye FPG and OGG1 Genes during Grain Germination

This research is about the profiling of barley (Hordeum vulgare L.), wheat (Triticum aestivum L.), and rye (Secale cereale L.) FPG and OGG1 genes during grain germination. During seed germination, reactive oxygen species accumulate, which leads to DNA damage. In the base excision repair (BER) system, the enzymes formamidopyrimidine DNA glycosylase (FPG) and 8-oxoguanine DNA glycosylase (OGG1), among others, are responsible for repairing such damage. We decided to check how the expression of genes encoding these two enzymes changes in germinating grains. Spring varieties of barley, wheat, and rye from the previous growing season were used in the study. Expression level changes were checked using Real-Time PCR. After analyzing the obtained results, the maximum expression levels of FPG and OGG1 genes during germination were determined for barley, wheat, and rye. The results of the study show differences in expression levels specific to each species. The highest expression was observed at different time points for each of them. There were no differences in the highest expression for FPG and OGG1 within one species. In conclusion, the research provides information on how the level of FPG and OGG1 gene expression changes during the germination process in cereals. This is the first study looking at the expression levels of these two genes in cereals.

8-oxoguanine DNA Glycosylase (OGG1) may be a Diagnostic Indicator of Diminished Ovarian Reserve (DOR)

BACKGROUND

Oxidative/antioxidant imbalance is considered a causal cause of diminished ovarian reserve (DOR). 8-oxyguanine DNA glycosylase (OGG1) has been reported to act as an antioxidant by binding non-catalytically to oxidation-induced DNA damage in the promoter region.

OBJECTIVE

This study aimed to evaluate serum OGG1 concentrations in patients with or without DOR and to explore the clinical value of OGG1 as a novel diagnostic indicator for DOR.

METHODS

Sixty-four women with DOR and seventy-eight women with normal ovarian reserve (NOR) from the reproductive medical center of Renmin Hospital of Wuhan University were included. Enzyme-linked immunosorbent assay (ELISA) kits were used to determine serum OGG1 levels in patients on 2-5 days of the menstrual cycle. Data regarding the enrolled patients were also obtained from the database of the hospital, including age, body mass index (BMI), anti-Müllerian hormone (AMH), etc. Results: OGG1 levels were increased in the DOR group (2.08 ± 0.70 vs 1.46 ± 0.47 nmol/L, P < 0.001) and negatively correlated with AMH levels (Spearman r = -0.586, P < 0.001). After adjusting for age and BMI, a negative association between OGG1 and AMH remained (β = -0.619, P < 0.001). ROC curve analysis showed that a cut-off value of 1.765 nmol/L had an appropriate sensitivity (81.30%) and specificity (76.90%) for discriminating individuals with and without DOR, with the area under the curve (95% CI) of 0.870 (0.814 to 0.926), P < 0.001.

CONCLUSION

We determined that serum OGG1 levels might be suggested as a new diagnostic indicator for DOR.

Inhibition of 8-oxoguanine DNA glycosylase (OGG1) expression suppresses polycystic ovarian syndrome via the NF-κB signaling pathway

It has been reported that oxidative stress and chronic inflammation may be involved in the pathogenesis of polycystic ovary syndrome (PCOS). 8-oxoguanine DNA glycosylase (OGG1) is the main glycosylase that catalyzes the excision of DNA oxidation products. In this study, we investigated the role and potential mechanisms of OGG1 in the development of PCOS. We first analyzed OGG1 levels in serum and follicular fluid (FF) of PCOS patients, and significantly elevated OGG1 levels were noted in PCOS patients. We similarly observed a significant upregulation of OGG1 expression levels in ovarian tissue of the dehydroepiandrosterone (DHEA)-induced PCOS rat model. In addition, increased apoptosis and increased production of reactive oxygen species (ROS) were observed after the addition of OGG1-specific inhibitor (TH5487) in human granulosa-like tumor cell line (KGN) cells following a concentration gradient, along with a significant decrease in mRNA levels of inflammatory factors such as CXCL2, IL-6, MCP1, IL-1β, and IL-18. Significant decreases in protein phosphorylation levels of P65 and IκBα were also observed in cells. In addition, we found a significant positive correlation between OGG1 and IL-6 expression levels in human and DHEA-induced PCOS rat models. In conclusion, our results suggest that OGG1 might be involved in the pathogenesis of PCOS by regulating the secretion of IL-6 through NF-κB signaling pathway, and there might be a balance between the inhibition of oxidative stress and the promotion of chronic inflammation by OGG1 on KGN cells.

Radon inhalation decreases DNA damage induced by oxidative stress in mouse organs via the activation of antioxidative functions

Radon inhalation decreases the level of lipid peroxide (LPO); this is attributed to the activation of antioxidative functions. This activation contributes to the beneficial effects of radon therapy, but there are no studies on the risks of radon therapy, such as DNA damage. We evaluated the effect of radon inhalation on DNA damage caused by oxidative stress and explored the underlying mechanisms. Mice were exposed to radon inhalation at concentrations of 2 or 20 kBq/m3 (for one, three, or 10 days). The 8-hydroxy-2'-deoxyguanosine (8-OHdG) levels decreased in the brains of mice that inhaled 20 kBq/m3 radon for three days and in the kidneys of mice that inhaled 2 or 20 kBq/m3 radon for one, three or 10 days. The 8-OHdG levels in the small intestine decreased by approximately 20-40% (2 kBq/m3 for three days or 20 kBq/m3 for one, three or 10 days), but there were no significant differences in the 8-OHdG levels between mice that inhaled a sham treatment and those that inhaled radon. There was no significant change in the levels of 8-oxoguanine DNA glycosylase, which plays an important role in DNA repair. However, the level of Mn-superoxide dismutase (SOD) increased by 15-60% and 15-45% in the small intestine and kidney, respectively, following radon inhalation. These results suggest that Mn-SOD probably plays an important role in the inhibition of oxidative DNA damage.

[Efficient screening for 8-oxoguanine DNA glycosylase binding aptamers via capillary electrophoresis]

8-氧代鸟嘌呤DNA糖基化酶(OGG1)是人体中重要的功能蛋白,在修复DNA氧化性损伤过程中起关键作用。氧化应激等引起的氧化损伤易导致炎症反应的发生,对OGG1的抑制可以一定程度上起到缓解作用;对癌细胞OGG1的抑制有望作为癌症治疗的新方法。目前的研究多集中于小分子对OGG1功能的影响和调控,而OGG1的适配体筛选尚未见报道。作为功能配体,适配体具有合成简单、高亲和力及高特异性等优点。该文筛选了OGG1的核酸适配体,结合毛细管电泳高效快速的优点建立了两种基于毛细管电泳-指数富集进化(CE-SELEX)技术的筛选方法:同步竞争法和多轮筛选法。同步竞争法利用单链结合蛋白(SSB)与核酸库中单链核酸的强结合能力,与目标蛋白OGG1组成竞争体系,并通过增加SSB浓度来增加竞争筛选压力,以去除与OGG1弱结合的核酸序列,一步筛选即可获得与OGG1强结合的核酸序列。多轮筛选法在相同孵育条件和电泳条件下,经3轮筛选获得OGG1的核酸适配体。比较两种筛选方法的筛选结果,筛选结果中频次最高的3条候选核酸适配体序列一致,其解离常数(K_D)值在1.71~2.64 μmol/L之间。分子对接分析结果表明候选适配体1(Apt 1)可能与OGG1中具有修复氧化性损伤功能的活性口袋结合。通过对两种筛选方法的对比,证明同步竞争法更加快速高效,对其他蛋白核酸适配体筛选方法的选择具有一定的指导意义。得到的适配体有望用于OGG1功能调控,以抑制其修复功能。

Development of a background signal suppression probe for 8-oxoguanine DNA glycosylase detection

8-oxoguanine DNA glycosylase (OGG), which plays a crucial role in base excision repair (BER), is an important biomarker. The existing highly sensitive fluorescent methods always need complicated amplification design. The method with high sensitivity and simple design at the same time is urgently needed. Here, we developed a highly sensitive detection method for OGG detection with lambda exonuclease and the background signal suppression probe. Through probe structure design, the steric hindrance and competitive binding effects successfully suppressed the background signal. We achieved sensitive detection of OGG with a simple design, and the limit of detection was 5.0 × 10^-4 U mL^-1. Moreover, the method was highly selective and successfully applied to OGG detection in biological samples, which shows the potential clinical application value.

8-Oxoguanine DNA Glycosylase (OGG1) Cys326 Variant: Increased Risk for Worse Outcome of Patients with Locally Advanced Rectal Cancer after Multimodal Therapy

Despite excellent loco-regional control by multimodal treatment of locally advanced rectal cancer, a substantial portion of patients succumb to this disease. As many treatment effects are mediated via reactive oxygen species (ROS), we evaluated the effect of single nucleotide polymorphisms (SNPs) in ROS-related genes on clinical outcome. Based on the literature, eight SNPs in seven ROS-related genes were assayed. Eligible patients (n = 287) diagnosed with UICC stage II/III rectal cancer were treated multimodally starting with neoadjuvant radiochemotherapy (N-RCT) according to the clinical trial protocols of CAO/ARO/AIO-94, CAO/ARO/AIO-04, TransValid-A, and TransValid-B. The median follow-up was 64.4 months. The Ser326Cys polymorphism in the human OGG1 gene affected clinical outcome, in particular cancer-specific survival (CSS). This effect was comparable in extent to the ypN status, an already established strong prognosticator for patient outcome. Homozygous and heterozygous carriers of the Cys326 variant (n = 105) encountered a significantly worse CSS (p = 0.0004 according to the log-rank test, p = 0.01 upon multiple testing adjustment). Cox regression elicited a hazard ratio for CSS of 3.64 (95% confidence interval 1.70-7.78) for patients harboring the Cys326 allele. In a multivariable analysis, the effect of Cys326 on CSS was preserved. We propose the genetic polymorphism Ser326Cys as a promising biomarker for outcome in rectal cancer.

Latent Membrane Protein 1 Promotes Tumorigenesis Through Upregulation of PGC1β Signaling Pathway

Natural killer/T-cell lymphoma (NKTCL) is an aggressive Epstein-Barr virus (EBV)-associated non-Hodgkin lymphoma with poor prognosis. In this study, we aimed to investigate the potential mechanism of latent membrane protein 1 (LMP1)-mediated tumorigenesis and provide a novel therapeutic strategy for targeting the EBV DNA genome. We found that LMP1 upregulated the expression of peroxisome proliferator-activated receptor-γ (PPARγ) coactivator-1β (PGC1β) through activation of nuclear factor-κB (NF-κB). Furthermore, the activated PGC1β upregulated the expression of 8-oxoguanine DNA glycosylase (OGG1) through the coactivation of nuclear respiratory factor 1 (NRF1) and GA-binding protein α (GABPα), preventing reactive oxygen species (ROS)-mediated base incision in the EBV genome and favoring its survival. Interruption of hexokinase domain component 1 (HKDC1) by either shRNA or Tf-D-HKC8 peptide suppressed the interaction of HKDC1 with voltage-dependent anion channel 1 (VDAC1), triggering mitochondrial dysfunction and excessive generation of ROS, thus resulting in EBV suppression through ROS-mediated DNA damage. Suppression of the EBV genome inhibited the expression of the LMP1/PGC1β/HKDC1/OGG1 signaling pathway, forming a positive feed forward loop for the generation of ROS, hence inhibiting the EBV genome and subsequent EBV-associated tumor development. We concluded that LMP1 triggers EBV-associated tumorigenesis through activation of the PGC1β pathway. This study provided a novel therapeutic strategy for the treatment of EBV-associated tumors by targeting HKDC1.

The correlation of combined OGG1, CYP1A1 and GSTP1 gene variants and risk of lung cancer of male Iraqi waterpipe tobacco smokers

Genetic polymorphisms of genes whose products are responsible for activities, such as xenobiotic metabolism, mutagen detoxification and DNA-repair, have been predicted to be associated with the risk of developing lung cancer (LC). The association of LC with tobacco smoking has been extensively investigated, but no studies have focused on the Arab ethnicity. Previously, we examined the association between genetic polymorphisms among Phase I and Phase II metabolism genes and the risk of LC. Here, we extend the data by examining the correlation of OGG1 Ser326Cys combined with CYP1A1 (Ile462Val and MspI) and GSTP1 (Ile105Val and Ala103Val) polymorphisms with the risk of LC. Polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) and gene sequencing were carried out for genotyping the OGG1 polymorphisms of 123 LC patients and 129 controls. No significant differences in the frequencies of the OGG1 mutant allele between patients and controls were found. The distributions of heterozygous Ser/Cys or Cys/Cys genotypes of OGG1 were not associated with the risk of LC either according to the histological types of LC or based on waterpipe tobacco (WP) smoking status. In contrast, the combined effect of OGG1 variants with CYP1A1 and GSTP1 variants revealed a significant correlation with the OGG1 Ser326Cys-CYP1A1 MspI variants pairing. This association was significant (p = 0.001) in individuals who carried homozygous or heterozygous variant type genotypes of both genes in a reference with carriers of both wild-type genotypes (wt/wt - wt/wt). The odds ratios were 2.99 (95% CI 1.67-5.36), 2.68 (95% CI 1.08-6.62), and 2.80 (95% CI 1.18-6.69) for those who carried (wt/wt - wt/vt + vt/vt), (wt/vt + vt/vt - wt/wt), and (wt/vt + vt/vt - wt/vt + vt/vt), respectively. The study suggests a limited correlation is present between carrying OGG1 Ser326Cys polymorphism and the risk of developing LC in Arab populations.

Induction of apoptosis in Ogg1-null mouse embryonic fibroblasts by GSH depletion is independent of DNA damage

Reactive oxygen species (ROS) within the cell are rapidly detoxified by antioxidants such as glutathione. Depletion of glutathione will therefore increase levels of intracellular ROS, which can lead to oxidative DNA damage and the induction of apoptosis. The working hypothesis was that Ogg1 null mouse embryonic fibroblasts (mOgg1^-/- MEFs) would be more sensitive in response to GSH depletion due to their deficiency in the removal of the oxidative DNA modification, 8-oxo-7,8-dihydroguanine (8-oxoG). Following GSH depletion, an increase in intracellular ROS and a subsequent induction of apoptosis was measured in mOgg1^-/- MEFs; as expected. Unexpectedly, an elevated basal level of ROS was identified in mOgg1^-/- MEFs compared to wild type MEFs; which we suggest is partly due to the differential expression of key anti-oxidant genes. The elevated basal ROS levels in mOgg1^-/- MEFs were not accompanied by a deficiency in ATP production or a large increase in 8-oxoG levels. Although 8-oxoG levels did increase following GSH depletion in mOgg1^-/- MEFs; this increase was significantly lower than observed following treatment with a non-toxic dose of hydrogen peroxide. Reconstitution of Ogg1 into mOgg1^-/- MEFs resulted in an increased viability following glutathione depletion, however this rescue did not differ between a repair-proficient and a repair-impaired variant of Ogg1. The data indicates that induction of apoptosis in response to oxidative stress in mOgg1^-/- MEFs is independent of DNA damage and OGG1-initiated DNA repair.

OGG1 methylation mediated the effects of cell cycle and oxidative DNA damage related to PAHs exposure in Chinese coke oven workers

Previous publications have indicated that polycyclic aromatic hydrocarbons (PAHs) exposures are associated with increased DNA damage and abnormal cell cycle arrest; however, the details of mechanisms remain largely unknown. This study aimed to quantify the associations of 8-oxoguanine DNA glycosylase (OGG1) methylation with urinary PAHs metabolites, DNA damage and cell cycle arrest, and further to assess the role of OGG1 methylation in mediating the association of urinary PAHs metabolites with DNA damage and cell cycle arrest. Urinary biomarkers of PAHs exposure and a marker of oxidative DNA damage (8-hydroxy-2'-deoxyguanosin, 8-OHdG) were measured by high performance liquid chromatography. Cell cycle of lymphocyte was analysed with flow cytometry and OGG1 methylation in venous blood was measured by pyrosequencing. After adjusting for covariates, urinary 1-OHP levels were positively associated with lymphocyte S phase arrest and oxidative DNA damage, while were negatively associated with G0/G1 phase arrest. OGG1 methylation was not only positively correlated with urinary 1-OHP in a dose-responsive manner (P trend = 0.008) but was also associated with G0/G1 phase arrest (OR: 0.63, 95% CI: 0.41-0.97), S phase arrest (OR: 1.55, 95% CI: 1.01-2.40) and oxidative DNA damage (OR: 1.71, 95% CI: 1.02-2.86). Mediation analysis estimated that OGG1 methylation mediated about 20% of associations between urinary 1-OHP levels and cell cycle arrest and oxidative DNA damage, respectively (all P < 0.05). Our findings suggested that urinary 1-OHP concentrations were associated with cell cycle arrest and oxidative DNA damage by a mechanism partly involving OGG1 methylation.

Association between the 8-oxoguanine DNA glycosylase gene Ser326Cys polymorphism and age-related cataract: a systematic review and meta-analysis

PURPOSE

To investigate the association between the 8-oxoguanine DNA glycosylase (OGG1) gene Ser326Cys (rs1052133) polymorphism and age-related cataract (ARC).

METHODS

MEDLINE and EMBASE were searched to identify potential studies published before May 19, 2017, investigating the association between the OGG1 gene Ser326Cys polymorphism and ARC risk. The quality of eligible studies was assessed using the Newcastle-Ottawa Scale tool. The association between the OGG1 gene Ser326Cys polymorphism and ARC was analyzed using meta-analysis. Publication bias and sensitivity analyses were also performed.

RESULTS

Six studies were included in this systematic review, and five of these studies with Hardy-Weinberg equilibrium were included in a meta-analysis. The sample size of the meta-analysis was 3716, including 1831 patients with cataract and 1885 controls. Odds ratios (ORs) were 0.67 (95% confidence interval (CI) 0.52-0.85), 0.90 (95% CI 0.54-1.51), 0.52 (95% CI 0.32-0.85) and 0.72 (95% CI 0.56-0.92) for recessive, dominant, additive and allele contrast models, respectively. Sensitivity analysis indicated that the results of the meta-analysis were robust. No publication bias was observed.

CONCLUSIONS

The OGG1 gene Ser326Cys polymorphism was associated with ARC risk.

Lack of any Association between the Hogg1 Ser326Cys Polymorphism and Breast Cancer Risk: a Systematic Review And Meta-Analysis Of 18 Studies

Background:

The human 8-oxoguanine DNA glycosylase (hOGG1) gene may be linked with cancer susceptibility. The aim of this study was to quantitatively summarize any association between the hOGG1 Ser326Cys polymorphism and breast cancer (BC) risk.

Materials and Methods:

A comprehensive search of the PubMed, Embase, and ISI web of knowledge databases for papers published before 1 October 2016 was conducted. Summary odds ratios (ORs) with corresponding 95 % confidence intervals (95 %CIs) were estimated, with fixed-effects or random-effects models when appropriate, to assess any association.

Results:

A total of 9,434 cases and 10,497 controls from 18 studies were included in this meta-analysis. When the eligible studies were pooled, there was no evidence found for a significant association between the hOGG1 Ser326Cys polymorphism and BC in in all genetic contrast models G vs. C (OR=1.19, 95% CI 0.92– 1.53), CG vs. CC (OR = 0.97, 95% CI 0.91-1.04, p = 0.46), GG vs. CC (OR = 1.11, 95% CI 0.91-1.35, p = 0.30), GG + CG vs. CC (OR = 0.98, 95% CI 0.92-1.05, p = 0.67), and GG vs. CG + CC (OR = 1.22, 95% CI 0.98-1.52, p = 0.07). According to subgroup analysis, we also did not find a significant association between the hOGG1 Ser326Cys polymorphism and BC risk in Asians and Caucasians considered separately.

Conclusions:

The current meta-analysis suggests that the hOGG1 Ser326Cys polymorphism is not significantly associated with BC risk.

Transforming growth factor-β and toll-like receptor-4 polymorphisms are not associated with fibrosis in haemochromatosis

AIM: To investigate the role of genetic polymorphisms in the progression of hepatic fibrosis in hereditary haemochromatosis.

METHODS: A cohort of 245 well-characterised C282Y homozygous patients with haemochromatosis was studied, with all subjects having liver biopsy data and DNA available for testing. This study assessed the association of eight single nucleotide polymorphisms (SNPs) in a total of six genes including toll-like receptor 4 (TLR4), transforming growth factor-beta (TGF-β), oxoguanine DNA glycosylase, monocyte chemoattractant protein 1, chemokine C-C motif receptor 2 and interleukin-10 with liver disease severity. Genotyping was performed using high resolution melt analysis and sequencing. The results were analysed in relation to the stage of hepatic fibrosis in multivariate analysis incorporating other cofactors including alcohol consumption and hepatic iron concentration.

RESULTS: There were significant associations between the cofactors of male gender (P = 0.0001), increasing age (P = 0.006), alcohol consumption (P = 0.0001), steatosis (P = 0.03), hepatic iron concentration (P < 0.0001) and the presence of hepatic fibrosis. Of the candidate gene polymorphisms studied, none showed a significant association with hepatic fibrosis in univariate or multivariate analysis incorporating cofactors. We also specifically studied patients with hepatic iron loading above threshold levels for cirrhosis and compared the genetic polymorphisms between those with no fibrosis vs cirrhosis however there was no significant effect from any of the candidate genes studied. Importantly, in this large, well characterised cohort of patients there was no association between SNPs for TGF-β or TLR4 and the presence of fibrosis, cirrhosis or increasing fibrosis stage in multivariate analysis.

CONCLUSION: In our large, well characterised group of haemochromatosis subjects we did not demonstrate any relationship between candidate gene polymorphisms and hepatic fibrosis or cirrhosis.

Impact of genetic polymorphisms in base excision repair genes on the risk of breast cancer in a Korean population

The contribution of single nucleotide polymorphisms (SNPs) in base excision repair (BER) genes to the risk of breast cancer (BC) was evaluated by focusing on two key genes: apurinic/apyrimidinic endonuclease 1 (APEX1) and 8-oxoguanine DNA glycosylase (OGG1). Genetic variations in the genes encoding these DNA repair enzymes may alter their functions and increase susceptibility to carcinogenesis. The aim of this study was to analyze polymorphisms in two BER genes, exploring their associations and particularly the combined effects of these variants on BC risk in a Korean population. Three SNPs of two BER genes were genotyped using the Illumina GoldenGate™ method. In total, 346 BC patients and 361 cancer-free controls were genotyped for these BER gene polymorphisms and analyzed for their correlation with BC risk in multiple logistic regression models. Multiple logistic regression models adjusted for age, family history of BC, and body mass index were used. The APEX1 Asp148Glu polymorphism was weakly associated with BC risk. The combined analysis among the BER genes, however, showed significant effects on BC risk. The APEX1 Asp148Glu carrier, in combination with OGG1 rs2072668 and OGG1 Ser326Cys, was strongly associated with an increased risk of BC. Moreover, the combination of the C-C haplotype of OGG1 with the APEX1 Asp148Glu genotype was also associated with an additive risk effect of BC [ORs=2.44, 2.87, and 3.50, respectively]. The combined effect of APEX1 Asp148Glu was found to be associated with an increased risk of BC. These results suggest that the combined effect of different SNPs within BER genes may be useful in predicting BC risk.

DNA repair mechanisms in dividing and non-dividing cells

DNA damage created by endogenous or exogenous genotoxic agents can exist in multiple forms, and if allowed to persist, can promote genome instability and directly lead to various human diseases, particularly cancer, neurological abnormalities, immunodeficiency and premature aging. To avoid such deleterious outcomes, cells have evolved an array of DNA repair pathways, which carry out what is typically a multiple-step process to resolve specific DNA lesions and maintain genome integrity. To fully appreciate the biological contributions of the different DNA repair systems, one must keep in mind the cellular context within which they operate. For example, the human body is composed of non-dividing and dividing cell types, including, in the brain, neurons and glial cells. We describe herein the molecular mechanisms of the different DNA repair pathways, and review their roles in non-dividing and dividing cells, with an eye toward how these pathways may regulate the development of neurological disease.

8-oxoguanine DNA glycosylases: one lesion, three subfamilies

Amongst the four bases that form DNA, guanine is the most susceptible to oxidation, and its oxidation product, 7,8-dihydro-8-oxoguanine (8-oxoG) is the most prevalent base lesion found in DNA. Fortunately, throughout evolution cells have developed repair mechanisms, such as the 8-oxoguanine DNA glycosylases (OGG), which recognize and excise 8-oxoG from DNA thereby preventing the accumulation of deleterious mutations. OGG are divided into three subfamilies, OGG1, OGG2 and AGOG, which are all involved in the base excision repair (BER) pathway. The published structures of OGG1 and AGOG, as well as the recent availability of OGG2 structures in both apo- and liganded forms, provide an excellent opportunity to compare the structural and functional properties of the three OGG subfamilies. Among the observed differences, the three-dimensional fold varies considerably between OGG1 and OGG2 members, as the latter lack the A-domain involved in 8-oxoG binding. In addition, all three OGG subfamilies bind 8-oxoG in a different manner even though the crucial interaction between the enzyme and the protonated N7 of 8-oxoG is conserved. Finally, the three OGG subfamilies differ with respect to DNA binding properties, helix-hairpin-helix motifs, and specificity for the opposite base.